Design factors in body armor include fiber durability, laminate durability, performance variability in large ceramic plates and low design margins that all contribute to reliability issues. Other specification issues include: cost, density and total system mass, flexibility, mobility, heat retention, and integration with load carrying systems. Testing on such systems includes testing of small arms and fragments such as: 7.62 mm caliber small arms threats including 7.62×39 mm M43 and 7.62×51 mm. Impact velocities may range from 500-1000 meters/second. Fragment threat simulators may be in the range of 2, 4, 16, 64, and 207 grams with velocities ranging from 500-3000 meters/second.
The current state of the art in rifle or small arms protection includes a large single ceramic plate typically of boron carbide (B4C) bonded to a rigid fiber mass of unidirectional laminate material typically of Ultra High Molecular Weight Polyethylene (UHMWPE). These systems offer good performance for high energy fragmentation threats and for many of the various 7.62 mm caliber rifle rounds both with steel and other hard bullet core materials. The arial density of these plates is in the 4.5-8 lb/ft2 range. In most cases there is an additional backing fiber layer of Arimid woven or UHMWPE materials in the 1 lb/ft2 range.
The result of attacks on U.S., coalition and Iraqi personnel show that while armor systems are providing greater protection to the areas of body covered, the exposed areas in the sides, shoulders, upper thighs and neck account for a higher percentage of the battle injuries and fatalities. Clearly there is a need for a protective system that can extend the area of effective body coverage without disproportionately increasing the user's burden in terms of weight or limited flexibility.
Boron carbide (B4C) is the material of choice for body armor because of its low density (2.52 g/cm3) and extreme hardness. It is the third hardest material known after diamond and cubic boron nitride. Porosity severely degrades the ballistic properties of ceramic armor as it acts as a crack initiator, and unfortunately, B4C has historically not sintered well. Sintering aids, e.g. graphite, improve sintering but degrade hardness and ballistic properties. Thus presently, B4C small arms protective inserts for personal armor are hot pressed to minimize porosity, typically to about 98% relative density, yielding acceptable performance. However, commercial hot pressing requires nesting of parts, which restricts the shape of the parts to plates or simple curves. These plates protect only the essential organs of the body. The area of coverage of body armor systems could be extended to additional body parts if boron carbide armor could be produced cost effectively in complex shapes, and if a suitable design incorporating such materials could combine the requisite ballistic protection with sufficient flexibility, without a substantial weight penalty.
Traditional systems with overlapping armor elements have not been able to provide the sought-after degree of flexure with the required continuous protection across fold lines of the garment or panel. Moreover, overlapping ceramic systems suffer from very high mass per unit area, which translates into weight in the protective panel or garment.